Rh110 (rhodamine 110)-derived caspase substrates are probably the most sensitive indicators widely used for the fluorimetric detection of various caspase activities. Cleavage of Rh110 peptides by caspases generates strongly fluorescent Rh110 that is monitored fluorimetrically at 510-530 nm with excitation of 488 nm, the most common excitation light source used in fluorescence instruments.